Gyp"sum (?), n. [L. gypsum, Gr. ; cf. Ar. jibs plaster, mortar, Per. jabsn lime.] Min.
A mineral consisting of the hydrous sulphate of lime (calcium). When calcined, it forms plaster of Paris. Selenite is a transparent, crystalline variety; alabaster, a fine, white, massive variety.
© Webster 1913.